Medical Device Probe with Source and Detector Sensors

ABSTRACT

A probe for a medical device with source and detector sensors is used to monitor or measure, or both, oxygen saturation levels in a tissue. In various specific implementations, the probe has at least two sources and at least one detector, at least one source and at least two detectors, and at least two sources and at least four detectors. A source of the probe is connected to at least one radiation source, which is external to the probe. A detector of the probe is connected to a photodetector, which is external to the probe.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation of U.S. patent applicationSer. No. 11/162,376, filed Sep. 8, 2005, which is incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical imaging systems thatmonitor oxygen levels in tissue. More specifically, the presentinvention relates to optical probes that include sources and detectorsthat are not symmetrically arranged on sensor heads of the opticalprobes.

Near-infrared spectroscopy has been used for noninvasive measurement ofvarious physiological properties in animal and human subjects. The basicprinciple underlying the near-infrared spectroscopy is thatphysiological tissues include various highly-scattering chromophores tothe near-infrared waves with relatively low absorption. Many substancesin a medium may interact or interfere with the near-infrared light wavespropagating therethrough. Human tissues, for example, include numerouschromophores such as oxygenated hemoglobin, deoxygenated hemoglobin,water, lipid, and cytochrome, where the hemoglobins are the dominantchromophores in the spectrum range of approximately 700 nanometers toapproximately 900 nanometers. Accordingly, the near-infraredspectroscope has been applied to measure oxygen levels in thephysiological medium such as tissue hemoglobin oxygen saturation andtotal hemoglobin concentrations.

Various techniques have been developed for the near-infraredspectroscopy, e.g., time-resolved spectroscopy (TRS), phase modulationspectroscopy (PMS), and continuous wave spectroscopy (CWS). In ahomogeneous and semi-infinite model, both TRS and PMS have been used toobtain spectra of an absorption coefficient and reduced scatteringcoefficient of the physiological medium by solving a photon diffusionequation, and to calculate concentrations of oxygenated and deoxygenatedhemoglobins as well as tissue oxygen saturation. CWS has generally beendesigned to solve a modified Beer-Lambert equation and to measurechanges in the concentrations of oxygenated and deoxygenatedhemoglobins.

Despite their capability of providing the hemoglobin concentrations aswell as the oxygen saturation, one major drawback of TRS and PMS is thatthe equipment is bulky and expensive. CWS may be manufactured at a lowercost but is limited in its utility because it cannot compute the oxygensaturation from the changes in the concentrations of oxygenated anddeoxygenated hemoglobins.

Optical diffusion imaging and spectroscopy (ODIS) allows tissue to becharacterized based on measurements of photon scattering and absorption.In tissue such as human tissue, near-infrared light is highly scatteredand minimally absorbed. Optical diffusion imaging is achieved by sendingoptical signals into tissue and measuring the corresponding diffusereflectance or transmittance on the tissue surface.

Scattering is caused by the heterogeneous structure of a tissue and,therefore, is an indicator of the density of a cell and the nuclear sizeof the cell. Absorption is caused by interaction with chromophores. ODISemits light into tissue through a sensor. The position of the lightsource which emits the light and a detector which detects the lightallows a depth of measurement to be determined. A ratio of oxyhemoglobinand deoxyhemoglobin may be used to allow for substantially real-timemeasurement of oxygen, e.g., oxygen saturation levels.

Within ODIS systems, sensors which come into contact with tissuesurfaces generally have optical fibers arranged thereon in asubstantially symmetric layout. That is, optical fibers that are coupledto light sources are arranged in a substantially symmetric orientationrelative to optical fibers that are coupled to light detectors. While asymmetric orientation is effective in allowing for oxygen saturationlevels to be measured, the manufacture of such sensor is oftendifficult, as the exact placement of the optical fibers within thesensor is crucial. Further, when the anatomy of tissue or underlyingstructure is not substantially symmetric, the use of a sensor with asymmetric orientation may not allow for accurate measurements to bereadily made.

Therefore, what is needed is a sensor that is relatively easy tomanufacture, and is arranged to be used on tissue which may not have asymmetric anatomy. That is, what is desired is a sensor with a layout ofoptical fibers for light sources and optical fibers for detectors thatfacilitates use with tissue having substantially any anatomy.

BRIEF SUMMARY OF THE INVENTION

A probe for a medical device with source and detector sensors is used tomonitor or measure, or both, oxygen saturation levels in a tissue. Invarious specific implementations, the probe has at least two sources andat least one detector, at least one source and at least two detectors,and at least two sources and at least four detectors. A source of theprobe is connected to at least one radiation source, which is externalto the probe. A detector of the probe is connected to a photodetector,which is external to the probe.

Further, in a specific implementation, a distance between the firstsource and the first detector is different from a distance between thesecond source and the first detector. In another specificimplementation, a distance between the first source and the firstdetector is different from a distance between the first source and thesecond detector.

When used, the probe is placed against or near tissue to be measured,radiation is emitted from one or more of the sources, reflected ortransmitted through the tissue, and received by one or more of thedetectors. Multiple different wavelengths of radiation may be emitted. Abeam combiner, external to the probe, is used to pass any one ofmultiple wavelengths of radiation or light (e.g., from two or morediodes, also external to the probe) to at least one source sensor at theprobe. The amount of the attenuation between the signal emitted andsignal detected is used in determining oxygen saturation levels.

The present invention relates to a probe with a sensor that supportssource fibers and detector fibers such that the source fibers have asubstantially nonsymmetric arrangement relative to the detector fibers.According to one aspect of the present invention, a sensor arrangementthat is suitable for use in an optical imaging system and is arranged tocontact a body such as tissue includes a first source structure, asecond source structure, and a detector arrangement. The first sourcestructure provides a first beam of light and the second source structureprovides a second beam of light.

The detector arrangement includes detector structures and receives thefirst beam of light and the second beam of light after the first beam oflight and the second beam of light are reflected off of the body. Thedetector arrangement is arranged to define a first axis, and a distancefrom the first source structure to the first axis is not equal to adistance from the second source structure to the first axis.

In one embodiment, a difference between the distance from the firstsource structure to the first axis and the distance from the secondsource structure is at least approximately 0.03 millimeters. In such anembodiment, the distance from the first source structure to the firstaxis may be approximately 0.020 millimeters and the distance from thesecond source structure to the first axis may be approximately 0.24millimeters.

In an embodiment, a probe with a sensor or a sensor head that has sourcestructures in a nonsymmetric orientation with respect to detectorstructures enables the sensor head to be utilized to monitor tissue withan underlying anatomy that is not substantially symmetric. The lack ofsymmetry also effectively loosens manufacturing tolerances associatedwith the manufacture of such sensor. Any attenuation associated with theoffset orientation of optical fibers that are coupled to light sourcesis typically compensated for through the use of software executing withrespect to an optical imaging system. Hence, the amount of compensationapplied may be relatively easily varied as needed to accommodateinaccuracies in the positioning of optical fibers with respect to thesensor.

According to another aspect of the present invention, a sensorarrangement that is suitable for use in an optical imaging systemincludes a first source structure that is arranged to provide a firstbeam of light and a second source structure that is arranged to providea second beam of light. The sensor arrangement also includes a detectorarrangement that has a first detector structure and a second detectorstructure. The detector arrangement is arranged to receive the firstbeam of light and the second beam of light after the first beam of lightand the second beam of light are reflected off of or transmitted throughtissue. An orientation of the first source structure with respect to thedetector arrangement is not symmetric relative to an orientation of thesecond source structure with respect to the detector arrangement.

According to yet another aspect of the present invention, a method fortaking an oxygen saturation measurement of tissue using an opticalsystem that utilizes a probe with a sensor head in which a first sourcestructure and a second source structure are offset relative to detectorstructures involves positioning the sensor head in contact with thetissue and transmitting light into the tissue through the first sourcestructure and the second source structure. The method also involvesreceiving reflected light from the tissue at the detector structuresthat includes attenuation characteristics, and processing the reflectedlight using a number of photodetectors. Processing the reflected lightusing the number of photodetectors includes compensating for theattenuation characteristics using an attenuation compensator.

In accordance with still another aspect of the present invention, aprobe which may be used as a part of an optical system to monitor oxygenlevels in tissue includes a coupling interface that allows the probe tobe coupled to light sources and detectors. A sensor head of the probe isarranged to contact the tissue, and supports a first source structure, asecond source structure, and a detector arrangement. The first sourcestructure and the second source structure are coupled to the lightsources via the coupling interface, while the detector arrangement iscoupled to the detectors through the coupling interface. An orientationof the first source structure relative to the detector arrangement isnot symmetric with respect to an orientation of the second sourcestructure relative to the detector arrangement.

In one embodiment, the detector arrangement includes detectorstructures. In such an embodiment, the detector arrangement receives thefirst beam of light and the second beam of light after the first beam oflight and the second beam of light are reflected off of or transmittedthrough the tissue. The detector arrangement defines a first axis thatpasses through each detector structure of the detector structures suchthat a distance from the first source structure to the first axis isunequal to a distance from the second source structure to the firstaxis.

In an embodiment, the invention is a probe including: a cable interface,the cable interface being adapted to allow the probe to be connected toat least two radiation sources and at least one photodetector, where theradiation sources and a first photodetector are external to the probe;and a sensor head including a first source structure, a second sourcestructure, and a first detector structure, the first source structureand the second source structure being arranged to be connected to theradiation sources via the cable interface, the first detector structurebeing arranged to be connected to the first photodetector via the cableinterface.

In an embodiment, the invention is a probe including: a cable interface,the cable interface being adapted to allow the probe to be connected toat least two radiation sources and a at least two photodetectors, wherethe radiation sources and a first and second photodetector are externalto the probe; and a sensor head including a first source structure, afirst detector structure, and a second detector structure, the firstsource structure being arranged to be connected to the radiation sourcesvia the cable interface, the first detector structure being arranged tobe connected to the first photodetector via the cable interface, thesecond detector structure being arranged to be connected to the secondphotodetector via the cable interface.

In an embodiment, the invention is a probe including: a cable interface,the cable interface being adapted to allow the probe to be connected toat least two radiation sources and at least one photodetector, where theradiation sources and a first, second, third, and fourth photodetectorare external to the probe; and a sensor head including a first sourcestructure, a second source structure, a first detector structure, asecond detector structure, a third detector structure, and a fourthdetector structure. The first source structure and the second sourcestructure is arranged to be connected to the radiation sources via thecable interface, the first detector structure is arranged to beconnected to the first photodetector via the cable interface, a seconddetector structure is arranged to be connected to a second photodetectorvia the cable interface, a third detector structure is arranged to beconnected to a third photodetector via the cable interface, and a fourthdetector structure is arranged to be connected to the fourthphotodetector via the cable interface.

Other objects, features, and advantages of the present invention willbecome apparent upon consideration of the following detailed descriptionand the accompanying drawings, in which like reference designationsrepresent like features throughout the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a block diagram representation of an optical imagingsystem with a sensor head which includes sources in an offsetarrangement relative to detectors in accordance with an embodiment ofthe present invention.

FIG. 1B shows a block diagram representation of an optical imagingsystem with a sensor head which includes sources in an offsetarrangement relative to detectors, i.e., optical imaging system 100 ofFIG. 1A, in accordance with an embodiment of the present invention.

FIG. 2A shows a sensor head with a pair of light sources that are in anoffset arrangement relative to a pair of detectors in accordance with anembodiment of the present invention.

FIG. 2B shows a sensor head with a pair of light sources that are in anoffset arrangement relative to a set of four detectors in accordancewith a first embodiment of the present invention.

FIG. 2C shows a sensor head with a pair of light sources that are in anoffset arrangement relative to a set of four detectors in accordancewith a second embodiment of the present invention.

FIG. 3 shows light sources and detectors that are associated with asensor head in accordance with an embodiment of the present invention.

FIG. 4 shows a process flow of utilizing a sensor head with lightsources that are in an offset arrangement relative to detectors inaccordance with an embodiment of the present invention.

FIG. 5 shows an optical imaging system that includes a console and adecoupleable probe with a sensor head with light sources that are in anoffset arrangement relative to detectors in accordance with anembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A sensor head which is such that optical fibers that are coupled tolight sources are arranged in an offset orientation relative to opticalfibers that are coupled to detectors allows the sensor head to beutilized in areas in which tissue being monitored is not substantiallysymmetric. Any attenuation associated with the offset orientation ofoptical fibers that are coupled to light sources is typicallycompensated for through software. Such a sensor head is relatively easyto manufacture in that the placement of optical fibers that are coupledto light sources is less rigid, i.e., any slight variation in theplacement of the optical fibers may be corrected for using the softwarethat compensates for attenuation. In addition, the use of software tocompensate for attenuation associated with the placement of opticalfibers on a sensor head essentially enables the sensor head to be usedwith both symmetric and asymmetric tissue anatomies.

As will be understood by those skilled in the art, a volume of tissuesubstantially immediately beneath a sensor head may either behomogeneous or inhomogeneous depending upon the actual anatomicalstructures contained within this volume. By way of example, when asensor head is positioned on skin overlying a thick region of adiposetissue, the distribution of signet cells and capillaries containingoxygenated hemoglobin is generally relatively uniform, i.e., symmetricand homogenous. However, a sensor head may be positioned over a tissuevolume in which underlying structure include arteries, veins, bone,tendon, cartilage, fascia, muscle, or pigmented lesions. Such tissue mayhave asymmetric anatomies that cause light to be reflected or absorbedasymmetrically due, for example, to regions that are either unusuallyreflective or absorptive. Software that compensates for attenuation mayeliminate readings associated with light that reflects off of structuressuch as bone. Optical fibers that are coupled to sources and arepositioned in a sensor head in an offset orientation relative to opticalfibers coupled to detectors may facilitate the transmission and readingof light that avoids structures such as bone. Hence, the use of offsetsource optical fiber orientations facilitate the creation of specializedsensor heads that may be used to measure oxygen saturation in manydifferent parts of a body.

FIG. 1A shows a block diagram representation of an optical imagingsystem with a sensor head that includes source arrangements arranged inan offset orientation relative to detector arrangements in accordancewith an embodiment of the present invention. An optical imaging system100 includes a unit 104 and a probe 108 that are coupled via aconnection interface 112. Connection interface 112 is generally alight-tight interconnection with a laser safety interlock that isarranged to substantially prevent laser light from being emitted throughconnection interface 112 when probe 108 is not coupled to unit 104.Connection interface 112 typically includes a panel connector (notshown) attached to unit 104 and a cable connector (not shown) attachedto probe 108.

Unit 104 includes a first light source 116 and a second light source120. First light source 116 and second light source 120, in thedescribed embodiment, are each dual wavelength light sources. In otherwords, first light source 116 provides two wavelengths of light andsecond light source 120 provides two wavelengths of light. First lightsource 116 and second light source 120 may each include a laser diodethat provides a light beam or pulse at a lower frequency and a laserdiode that provides a light beam or pulse at a higher frequency. By wayof example, first light source 116 and second light source 120 may eachinclude a laser diode that produces visible red light of anapproximately 690-nanometer wavelength and a laser diode that producesnear-infrared light of an approximately 830-nanometer wavelength. Itshould be appreciated, however, that the wavelengths of light producedby laser diodes associated with first light source 116 and second lightsource 120 may vary widely.

Light emitted by first light source 116 and light emitted by secondlight source 120 is provided to a beam combiner 124 via optical fibers(not shown). Each laser diode associated with first light source 116 andeach laser diode associated with second light source 120 is provided ona separate optical fiber (not shown). Beam combiner 124 effectivelymerges the light from the laser diodes of first light source 116 andmerges the light from the laser diodes of second light source 120. Themerged light is then provided via output fibers (not shown) toconnection interface 112. The output fibers are arranged to allow themerged or combined light to be homogenized to ensure that the light issubstantially uniformly distributed across the output fibers when thelight enters connection interface 112.

Through connection interface 112, light is provided to a sensor head 128of probe 108. Within sensor head 128, optical fibers (not shown) providethe merged light associated with first light source 116 and the mergedlight associated with second light source 120 to a surface of sensorhead 128 that is arranged to come into contact with tissue 132. Theoptical fibers (not shown) are positioned such that they have an offsetorientation with respect to optical fibers (not shown) that areassociated with photodetectors 136 within unit 104. The orientation ofsource optical fibers and detector optical fibers will be describedbelow with respect to FIGS. 2A-2C.

When sensor head 128 causes light to be transmitted into tissue 132, thereflected light is collected by optical detector fibers (not shown) thatare coupled to photodetectors 136. In general, at least twophotodetectors 136 are included within unit 104 and are configured to besensitive to the light which is transmitted by first light source 116and second light source 120. An attenuation compensator 140 within unit104 is generally arranged to compensate for any attenuation in thereflected light that results from the offset orientation of sourceoptical fibers (not shown) relative to detector optical fibers (notshown). In one embodiment, attenuation compensator 140 effectivelyprovides compensation using a mathematical algorithm that constructsratios in which attenuation coefficients may be found in both anumerator and a denominator and hence, may be canceled out. Such ratiosmay use light intensities as detected by photodetectors 136 in such away that attenuation factors have little effect on the evaluation ofoptical properties of tissue 132 beneath sensor head 128. It should beappreciated that attenuation compensator 140 may generally besubstantially incorporated into software or firmware that executes analgorithm that determines oxygen saturation levels.

FIG. 1B shows a block diagram representation of optical imaging system100 of FIG. 1A which shows the path of light emitted by light sources,i.e., first light source 116 and second light source 120 of FIG. 1A, inaccordance with an embodiment of the present invention. When first lightsource 116 emits light at two wavelengths, light of the first wavelength152 a and light of the second wavelength 152 b are provided to beamcombiner 124 which effectively merges the light into a light stream 152c that is provided to sensor head 128, e.g., through optical sourcefibers. Similarly, when second light source 120 emits light at twowavelengths, light of the first wavelength 156 a and light of the secondwavelength 156 b are merged into a light stream 156 c by beam combiner124 that is provided to sensor head 128. Light streams 152 c, 156 c aretransmitted into tissue 132 reflect off of tissue 132, through sensorhead 128 to photodetectors 136.

As previously mentioned, optical source fibers are arranged such that ata surface of a sensor head that is arranged to come into contact withtissue, the optical source fibers have an offset orientation relative tooptical detector fibers. With reference to FIG. 2A, the orientation ofsource fibers with respect to detector fibers will be described inaccordance with an embodiment of the present invention. A sensor head200, which may be of substantially any shape or size, is a part of aprobe that is a part of an overall system that measures oxygensaturation levels in tissue. Sensor head 200 is arranged to accommodatesource arrangements 204 a, 204 b, and detector arrangements 208 a, 208b. For ease of discussion, although source arrangements 204 a, 204 b aregenerally fiber optic cables or optical fibers coupled to light sourcesand detector arrangements 208 a, 208 b are generally fiber optic cablesor optical fibers coupled to photodetectors, source arrangements 204 a,204 b are referred to in this application as sources and detectorarrangements 208 a, 208 b are referred to in this application asdetectors.

Sources 204 a, 204 b are arranged such that they are in an offsetarrangement relative to detectors 208 a, 208 b. That is, source 204 aand source 204 b are not equidistant to detectors 208 a, 208 b relativeto at least one axis. Detectors 208 a, 208 b are arranged such that acenterline 214 of detectors 208 a, 208 b is approximately parallel to anx-axis 212 a. Typically, centerline 214 passes through a centerpoint ofeach detector 208 a, 208 b. Sources 204 a, 204 b are arranged such thata centerline 216 of source 204 a is parallel to a centerline 218 ofsource 204 b, but is not coincident with centerline 218. Centerline 216passes through a centerpoint of source 204 a and is parallel to x-axis212 a, while centerline 218 passes through a centerpoint of source 204 band is parallel to x-axis 212 a.

A distance y1 between centerline 214 and centerline 216 along a y-axis212 b differs from a distance y2 between centerline 214 and centerline218. Although distance y2 is shown as being greater than distance y1, itshould be appreciated that distance y1 may instead be greater than y2.The difference between distance y2 and distance y1 is generallycharacteristic of the offset arrangement, or substantially unbalancedarrangement, of sources 204 a, 204 b relative to detectors 208 a, 208 b.In other words, there is effectively a lack of symmetry in the placementof sources 204 a, 204 b.

In general, more than two detectors may be used in conjunction with apair of detectors to monitor oxygen saturation in tissue. By way ofexample, three or four detectors may be used to detect light that isprovided by a pair of sources and is reflected off of a tissue surface.It should be appreciated that some of the light may be reflected fromtissue at various depths beneath the tissue surface. That is, light maybe reflected off the tissue surface and off of tissue that underlies thesurface. The tissue that underlies the surface and allows light to bereflected may be as deep as approximately one centimeter below thesurface of the tissue. FIG. 2B shows a sensor head which is arranged toinclude a pair of sources or, more specifically, source arrangements andfour detectors or, more specifically, detector arrangements, inaccordance with an embodiment of the present invention. A sensor head220 includes four detectors 228 a-d which are arranged such thatcenterpoints of detectors 228 a-d are substantially aligned along acenterline 234 that is substantially parallel to an x-axis 232 a. Sensorhead 220 also includes sources 224 a, 224 b which each include acenterpoint. A centerline 236 that is parallel to x-axis 232 a passesthrough the centerpoint of source 224 a, and a centerline 238 that isparallel to x-axis 232 a passes through the centerpoint of source 224 b.

In the described embodiment, a distance y1 along a y-axis 232 b betweencenterline 234 and centerline 236 is not equal to a distance y2 alongy-axis 232 b between centerline 234 and centerline 238. Distance y1 maybe approximately 0.2 millimeters, as for example approximately 0.197millimeters, while distance y2 may be approximately 0.24 millimeters, asfor example 0.236 millimeters. It should be appreciated that distance y1and distance y2 may vary widely depending upon any number of factors.The factors include, but are not limited to, the overall size of sources224 a, 224 b and detectors 228 a-d, the overall size of sensor head 220,and the application for which sensor head 220 is intended. Whiledistance y2 is shown as being greater than distance y1, distance y1 mayinstead be greater than distance y2. In general, the difference betweendistance y2 and distance y1 is at least approximately 0.3 millimeters.For example, distance y2 and distance y1 may differ by approximately 1.0millimeter.

The positioning of sources 224 a, 224 b and detectors 228 a-d may varywidely. By way of example, for an embodiment in which sources 224 a, 224b and detectors 228 a-d are each approximately 1.0 millimeter indiameter, centerpoints of sources 224 a, 224 b may be separated by adistance d2 that is approximately 0.22 millimeters relative to x-axis232 a and by a distance y4 that is approximately 0.04 millimeters.Detectors 228 a-d may be arranged such that centerline 234 is offsetfrom a top edge of sensor head 220 by a distance y3 that isapproximately 0.06 millimeters, and such that adjacent detectors 228 a-dare separated by a distance d1 that is between approximately 0.06millimeters to approximately 0.07 millimeters. Sensor head 220 may havea width of approximately 0.34 millimeters along x-axis 232 a and aheight of approximately 0.49 millimeters along y-axis 232 b whendetectors 228 a-d and sources 224 a, 224 b are spaced as describedabove. However, sensor head 220 generally has dimensions that may varywidely, e.g., dimensions which may vary depending upon the applicationfor which sensor head 220 is intended.

While a lack of symmetry in the positioning of sensors relative todetectors has been described as being such that distances betweensensors and detectors are not equal relative to a y-axis, a lack ofsymmetry may instead or additionally have a lack of symmetry relative toan x-axis. Referring next to FIG. 2C, a sensor head that includes a pairof sources which are in an offset arrangement relative to a set of fourdetectors with respect to an x-axis will be described. A sensor head 240includes four detectors 248 a-d, although the number of detectors 248a-d may vary. Detectors 248 a-d are arranged such that a centerline 254is substantially parallel to an x-axis 252 a and passes through thecenterpoint of each detector 248 a-d. A first detector 248 a and a lastdetector 248 d, i.e., the detectors which are farthest apart relative tox-axis 252 a, are used to define a central bisecting line 262 ofdetectors 248 a-d. Central bisecting line 262 is parallel to a y-axis252 b, and is arranged such that a distance x3 from the centerpoint ofdetector 248 a to central bisecting line 262 is substantially equal to adistance x4 from the centerpoint of detector 248 d to central bisectingline 262. That is, central bisecting line 262 is arranged to passthrough a central midpoint between the centerpoint of detector 248 a andthe centerpoint of detector 248 d such that central bisecting line 262is substantially perpendicular to centerline 254.

As shown, a centerpoint of a first source 244 a and the centerpoint offirst detector 248 a are aligned along a centerline 257 that issubstantially parallel to a y-axis 252 b. Similarly, a centerpoint of asecond source 244 b and the centerpoint of last detector 248 d arealigned along a centerline 259 that is substantially parallel to y-axis252 b. It should be appreciated, however, that centerline 257 may notnecessarily pass through the centerpoint of first detector 248 a, andcenterline 259 may not necessarily pass through the centerpoint of lastdetector 248 d. That is, centerline 257 is effectively a line that issubstantially parallel to y-axis 252 b and passes through first source244 a, while centerline 259 is effectively a line that is substantiallyparallel to y-axis 252 b and passes through second source 244 b.

A distance x1 between centerline 257 and central bisecting line 262 isnot equal to a distance x2 between centerline 259 and central bisectingline 262. In other words, first source 244 a and second source 244 b arenot equidistant from central bisecting line 262. Hence, sources 244 a,244 b are positioned in an offset or unbalanced orientation relative tox-axis 252 a.

Sources are typically arranged to emit light of specific wavelengths. Asdiscussed above, light of a lower wavelength emitted by a source mayhave a wavelength of approximately 690 nanometers, while light of ahigher wavelength emitted by the source may have a wavelength ofapproximately 830-nanometers. FIG. 3 shows light sources and detectorsthat are associated with a sensor head in accordance with an embodimentof the present invention. A first source may include a laser diode 302 athat produces light at a wavelength of approximately 690 nanometers aswell as a laser diode 302 b that produces light at a wavelength ofapproximately 830 nanometers. Similarly, a second source may include alaser diode 306 a that produces light at a wavelength of approximately690 nanometers as well as a laser diode 306 b that produces light at awavelength of approximately 830 nanometers.

A beam combiner 310 is arranged to enable light emitted by laser diodes302 a, 302 b to be merged onto an optical fiber 312 that is provided toa sensor head 322. Beam combiner 310 is also arranged to enable lightemitted by laser diodes 306 a, 306 b to be merged onto an optical fiber316 that is provided to sensor head 322. Light transmitted by fibers312, 316 through a tissue or other surface is reflected, and thereflected light is effectively captured on optical fibers 324 whichprovide the reflected light to photodetectors 318. Photodetectors 318are arranged to be sensitive to light with wavelengths of approximately690 nanometers and approximately 830 nanometers, and typically have arelatively high gain.

With reference to FIG. 4, one method of monitoring oxygen saturation intissue using an oximeter with a sensor head in which sources are in anoffset orientation relative to detectors will be described in accordancewith an embodiment of the present invention. A process 400 of using anoximeter begins at step 404 in which a probe, i.e., a probe thatincludes a sensor head in which sources are positioned in an offsetorientation relative to detectors, is applied against tissue. Once thesensor head is positioned in contact with tissue, a first source S1associated with the probe sends a lower wavelength pulse of light intothe tissue in step 408. The first source S1 may include a laser diodethat produces an approximately 690-nanometer wavelength of visible redlight, as discussed above, although the lower wavelength of lightproduced by the first source S1 may vary. In general, first source S1 isa source arrangement that produces light at two wavelengths. Hence,first source S1 may include two substantially separate laser diodes thatproduce light at two wavelengths.

In step 412, a detector arrangement associated with the probe detectsthe approximately 690-nanometer light. As discussed above, when theapproximately 690-nanometer light is transmitted into the tissue, theapproximately 690-nanometer light is reflected into the detectorarrangement such that the detectors, e.g., the photodetectors, includedin the detector arrangement collect the reflected light. A second sourceS2 then sends a lower wavelength pulse of light in step 416 which, inthe described embodiment, is an approximately 690-nanometer pulse oflight. The detector arrangement detects and collects the approximately690-nanometer reflected light in step 420.

Once the lower wavelength light is transmitted by both the first sourceS1 and the second source S2, the first source S1 sends a higherwavelength pulse of light into the tissue in step 424. The higherwavelength pulse of light may be an approximately 830-nanometernear-infrared light produced by a laser diode included in first sourceS1. After the approximately 830-nanometer pulse of light is transmittedinto the tissue and reflected, the process flow moves to step 428 inwhich the detector arrangement detects the reflected light.

The second source S2 sends a higher wavelength pulse of light, e.g.,light with an approximately 830-nanometer wavelength, in step 432 thatis then reflected off of the tissue and reflected into the detectorarrangement in step 436. Once the detector arrangement has receivedreflected light from both sensors at both the lower wavelength and thehigher wavelength, the data acquisition arrangement of the oximeterprocesses information associated with the received reflected light instep 440. Processing the received reflected light may include executingsoftware or firmware that accounts for or otherwise compensates forattenuation associated with the reflected light in order to determine anoxygen level associated with the tissue. Once the data acquisitionarrangement processes the information, the process of monitoring anoxygen saturation level of tissue is completed. It should be understood,however, the steps of FIG. 4 may be repeated to allow for thesubstantially continuous monitoring of an oxygen saturation level.

An oximeter which utilizes a probe with a sensor head of the presentinvention may include a portable console unit to which the probe may becoupled. As shown in FIG. 5, a console 500 may include a screen 504 thatis arranged to display the oxygen saturation level of tissue that isbeing monitored. Screen 504, which may be a touch screen, may also bearranged to indicate when a probe 520 is in use and to provide warningsto a user that indicate when a monitored oxygen saturation level ispotentially problematic.

Console 500 includes a panel connector 508 to which a connector 528 ofprobe 520 may be connected to allow a sensor head 530 of probe 520 to beused to monitor oxygen saturation levels. Fiber optic cables (not shown)which are used to allow light to pass between connector 528 and sensorhead 530 of probe 520 are substantially encased in a cable jacket 534.Console 500 and probe 520 may be a part of the ODISsey™ Tissue Oximeteravailable commercially from ViOptix, Inc. of Fremont, Calif. ODISsey isa trademark of ViOptix.

Although only a few embodiments of the present invention have beendescribed, it should be understood that the present invention may beembodied in many other specific forms without departing from the spiritor the scope of the present invention. By way of example, thewavelengths emitted by light sources have been described as beingapproximately 690 nanometers and approximately 830 nanometers. However,substantially any wavelengths may be emitted by the light sources.

The probe on which a sensor head is mounted may have a variety ofdifferent configurations. For example, the probe may include a handpiece which facilitates spot measurements of tissue. Additionally, theconfiguration of a sensor head may also vary depending upon theparticular application for which the sensor head is to be used.

A probe, e.g., a fiber optic probe, on which a sensor head is mounteduses fiber optic cable to carry an optical signal to and from tissue.The fiber optic cable may be of any length, and may contain one dualwavelength source fiber for each source and one detector fiber for eachdetector. In one embodiment, the fiber optic cable may be approximatelythree meters long, and the source and detector fibers may each havediameters of approximately one millimeter.

A centerpoint of a source optical fiber and a centerpoint of a detectoroptical fiber have generally been described as being centerpoints offibers that are substantially circular in orientation. It should beappreciated that in some instances, when a fiber is not substantiallycircular in orientation, the centerpoint may be an approximatecenterpoint of the fiber.

The steps associated with the various methods of the present inventionmay be widely varied. Steps may be added, altered, removed, andreordered without departing from the spirit or the scope of the presentinvention. Therefore, the present examples are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given in this application, but may be modified within thescope of the appended claims.

This description of the invention has been presented for the purposes ofillustration and description. It is not intended to be exhaustive or tolimit the invention to the precise form described, and manymodifications and variations are possible in light of the teachingabove. The embodiments were chosen and described in order to bestexplain the principles of the invention and its practical applications.This description will enable others skilled in the art to best utilizeand practice the invention in various embodiments and with variousmodifications as are suited to a particular use. The scope of theinvention is defined by the following claims.

1. A probe for a medical device comprising: a cable interface, the cableinterface being adapted to allow the probe to be coupled to a pluralityof radiation sources and at least one photodetector, wherein theradiation sources and a first photodetector are external to the probe;and a sensor head comprising a first source structure, a second sourcestructure, and a first detector structure, the first source structureand the second source structure being arranged to be coupled to theradiation sources via the cable interface, and the first detectorstructure being arranged to be coupled to the first photodetector viathe cable interface.
 2. The probe of claim 1 wherein the first detectorstructure and the first source structure have the same cross-sectionalarea.
 3. The probe of claim 1 wherein the probe comprises a seconddetector structure being arranged to be coupled to a secondphotodetector via the cable interface, and the second photodetector isexternal to the probe.
 4. The probe of claim 3 wherein a first distanceis between the first source structure and the first detector structure,a second distance is between the first source structure and the seconddetector structure, a third distance is between the second sourcestructure and the first detector structure, a fourth distance is betweenthe second source structure and the second detector structure, the firstdistance is not equal to the second, third, and fourth distances, thesecond distance is not equal to the third and fourth distances, and thethird distance is not equal to the fourth distance.
 5. The probe ofclaim 4 wherein the fourth distance is greater than the first distance.6. The probe of claim 4 wherein the fourth distance is greater than thefirst distance by at least about 0.3 millimeters.
 7. The probe of claim4 wherein a difference between the first and fourth distances is in arange from about 0.3 millimeters to about 1 millimeter.
 8. The probe ofclaim 1 wherein a first distance between the first detector structureand the first source structure is different from a second distancebetween the first detector structure and the second source structure. 9.The probe of claim 1 wherein the first source structure, second sourcestructure, and first detector structure are on a plane of the probe. 10.A medical device comprising a probe of claim 1 and a beam combiner,external to the probe, coupled to the first source structure and theradiation sources via the cable interface.
 11. The medical device ofclaim 10 wherein the beam combiner comprises a first input, coupled to afirst radiation source of a first wavelength, and a second input,coupled to a second radiation source of a second wavelength, differentfrom the first wavelength.
 12. The probe of claim 1 wherein each sourcestructure is coupled to at least two radiation sources.
 13. The probe ofclaim 1 wherein the radiation sources emit radiation for at least twodifferent wavelengths.
 14. The probe of claim 1 comprising a cablecoupling the sensor head to the cable interface, and the cable comprisesat least two optical fibers.
 15. The probe of claim 14 wherein the cablecomprises at least one optical fiber for each detector structure andeach source structure.
 16. The probe of claim 14 wherein a length of thecable is at least about 3 meters.
 17. A medical device comprising aprobe of claim 1 and a system console, external to the probe, comprisingthe radiation sources and at least one photodetector, and a systemconsole interface being adapted to couple to the cable interface of theprobe.
 18. The medical device of claim 17 wherein the system consolecomprises a screen that shows oxygen saturation information for tissuebeing monitored using the probe.
 19. A medical device that measuresoxygen saturation of a tissue comprising a probe of claim
 1. 20. A probefor a medical device comprising: a cable interface, the cable interfacebeing adapted to allow the probe to be coupled to a plurality ofradiation sources and a plurality of photodetectors, wherein theradiation sources and a first and second photodetector are external tothe probe; and a sensor head comprising a first source structure, afirst detector structure, and a second detector structure, the firstsource structure being arranged to be coupled to the radiation sourcesvia the cable interface, the first detector structure being arranged tobe coupled to the first photodetector via the cable interface, and thesecond detector structure being arranged to be coupled to the secondphotodetector via the cable interface.
 21. The probe of claim 20 whereinthe first detector structure and the first source structure have thesame cross-sectional area.
 22. The probe of claim 20 wherein the probecomprises a second source structure coupled to the radiation sources,each radiation source providing a different wavelength of light.
 23. Theprobe of claim 20 wherein a first distance between the first sourcestructure and the first detector structure is different from a seconddistance between the first source structure and the second detectorstructure.
 24. The probe of claim 20 wherein the first source structure,first detector structure, and second detector structure are on a planeof the probe.
 25. A medical device comprising a probe of claim 20 and abeam combiner, external to the probe, coupled to the first sourcestructure and the radiation sources via the cable interface.
 26. Themedical device of claim 25 wherein the beam combiner comprises a firstinput, coupled to a first radiation source of a first wavelength, and asecond input, coupled to a second radiation source of a secondwavelength, different from the first wavelength.
 27. The probe of claim20 wherein the first source structure is coupled to at least tworadiation sources.
 28. The probe of claim 20 wherein the radiationsources emit radiation for at least two different wavelengths.
 29. Theprobe of claim 20 comprising a cable coupling the sensor head to thecable interface, wherein the cable comprises at least two opticalfibers.
 30. The probe of claim 29 wherein the cable comprises at leastone optical fiber for each detector structure and each source structure.31. The probe of claim 29 wherein a length of the cable is at leastabout 3 meters.
 32. A medical device comprising a probe of claim 20 anda system console, external to the probe, comprising the radiationsources and photodetectors, and a system console interface being adaptedto couple to the cable interface of the probe.
 33. The medical device ofclaim 32 wherein the system console comprises a screen that shows oxygensaturation information for tissue being monitored using the probe.
 34. Amedical device that measures oxygen saturation of a tissue comprising aprobe of claim
 20. 35. A probe for a medical device comprising: a cableinterface, the cable interface being adapted to allow the probe to becoupled to a plurality of radiation sources and at least onephotodetector, wherein the radiation sources and a first, second, third,and fourth photodetector are external to the probe; and a sensor headcomprising a first source structure, a second source structure, a firstdetector structure, a second detector structure, a third detectorstructure, and a fourth detector structure, the first source structureand the second source structure being arranged to be coupled to theradiation sources via the cable interface, the first detector structurebeing arranged to be coupled to the first photodetector via the cableinterface, a second detector structure being arranged to be coupled to asecond photodetector via the cable interface, a third detector structurebeing arranged to be coupled to a third photodetector via the cableinterface, and a fourth detector structure being arranged to be coupledto the fourth photodetector via the cable interface.
 36. The probe ofclaim 35 wherein the first detector structure and the first sourcestructure have the same cross-sectional area.
 37. The probe of claim 35wherein the first, second, third, and fourth detector structures arearranged in a line.
 38. The probe of claim 35 wherein a first distanceis between the first source structure and the first detector structure,a second distance is between the first source structure and the seconddetector structure, a third distance is between the second sourcestructure and the first detector structure, a fourth distance is betweenthe second source structure and the second detector structure, a fifthdistance is between the first source structure and third detectorstructure, a sixth distance is between the first source structure andfourth detector structure, a seventh distance is between the secondsource structure and third detector structure, an eighth distance isbetween the second source structure and fourth detector structure, thefirst distance is not equal to the second, third, fourth, fifth, sixth,seventh, and eighth distances, the second distance is not equal to thethird, fourth, fifth, sixth, seventh, and eighth distances, the thirddistance is not equal to the fourth, fifth, sixth, seventh, and eighthdistances, the fourth distance is not equal to the fifth, sixth,seventh, and eighth distances, the fifth distance is not equal to thesixth, seventh, and eighth distances, the sixth distance is not equal tothe seventh, and eighth distances, and the seventh distance is not equalto the eighth distance.
 39. The probe of claim 38 wherein the first,second, third, and fourth detector structures are arranged in a line,and the third and fourth detector structures are between the first andsecond detector structures.
 40. The probe of claim 39 wherein the fourthdistance is greater than the first distance.
 41. The probe of claim 39wherein the fourth distance is greater than the first distance by atleast about 0.3 millimeters.
 42. The probe of claim 39 wherein adifference between the first and fourth distances is in a range fromabout 0.3 millimeters to about 1 millimeter.
 43. A medical devicecomprising a probe of claim 35 and a beam combiner, external to theprobe, coupled to the first source structure and the radiation sourcesvia the cable interface.
 44. The medical device of claim 43 wherein thebeam combiner comprises a first input, coupled to a first radiationsource of a first wavelength, and a second input, coupled to a secondradiation source of a second wavelength, different from the firstwavelength.
 45. The probe of claim 35 comprising a cable coupling thesensor head to the cable interface, and the cable comprises at least oneoptical fiber for each detector structure and each source structure. 46.The probe of claim 35 wherein the cable interface comprises at least anend for an optical fiber for each detector structure and each sourcestructure.
 47. The probe of claim 45 wherein a length of the cablebetween the sensor head and cable interface is at least about 3 meters.48. A medical device comprising a probe of claim 38 and a beam combiner,external to the probe, coupled to the first source structure and theradiation sources via the cable interface, the beam combiner comprises afirst input, coupled to a first radiation source of a first wavelength,and a second input, coupled to a second radiation source of a secondwavelength, different from the first wavelength, and the cable interfacecomprises at least an end for an optical fiber for each detectorstructure and each source structure.
 49. The medical device of claim 48wherein the first, second, third, and fourth detector structures arearranged in a line, the third and fourth detector structures are betweenthe first and second detector structures, and the fourth distance isgreater than the first distance by at least about 0.3 millimeters. 50.The medical device of claim 49 comprising: a system console, external tothe probe, comprising the first radiation source, second radiationsource, first photodetector, second photodetector, third photodetector,fourth photodetector, beam combiner, and a system console interfacebeing adapted to couple to the cable interface of the probe.
 51. Amedical device comprising a probe of claim 35 and a system console,external to the probe, comprising the radiation sources andphotodetectors, and a system console interface being adapted to coupleto the cable interface of the probe.
 52. The medical device of claim 51wherein the system console comprises a screen that shows oxygensaturation information for tissue being monitored using the probe.
 53. Amedical device that measures oxygen saturation of a tissue comprising aprobe of claim 35.